1. Technical Field
Exemplary aspects of the present disclosure generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a plotter, and more particularly, to an image forming apparatus including a photosensitive member on which an electrophotographic process is performed to form an image on a recording medium.
2. Description of the Related Art
In a known electrophotographic image forming apparatus, first, a document reader reads a document image, and subsequently, an electrostatic latent image bearing member of an image forming section is illuminated with light in accordance with the document image. Furthermore, the electrostatic latent image is developed with toner, thereby forming a visible image, known as a toner image. The toner image is transferred onto various kinds of recording media such as paper delivered from a sheet supply section. The transferred toner image is fixed on a recording medium and discharged onto an output section of the image forming apparatus.
The image forming section of the image forming apparatus employs an electrophotographic method using a negative-charge toner, a negative-charge photosensitive member, and an intermediate transfer member.
In such an image forming section of the image forming apparatus, when initializing operations such as a printing operation, a development section is supplied with a voltage (positive voltage) opposite that of the original voltage in order to prevent formation of a magnetic brush which is a cluster of developer formed in a form of brush until the charged portion (negative charge) of the photosensitive member arrives at the development section. After the charged portion of the photosensitive member arrives at the development section, generally, the development section is supplied with the original voltage (negative voltage).
In order to keep the surface potential of the photosensitive member around zero (0) V until the charged portion of the photosensitive member arrives at the development section, generally, the surface potential of the photosensitive member is electrically discharged in advance before stopping driving of the printing operation or the like. Thus, if the surface potential (negative) of the photosensitive member is relatively high at start of driving, the difference in the potential (development potential) between the photosensitive member and the development is significant at start of driving (development section, positive), worsening contamination of a non-image formation area also known as background fogging of the photosensitive member and hence causing unnecessary consumption of developing agent.
In order to reduce the size of the apparatus, it is necessary to reduce the width of an image forming unit as much as possible, and it is known that reducing the width of an exposure device such as a light emitting diode (LED) and a laser diode (LD) shorter than the width of the photosensitive member can reduce the width of the image forming unit. If the exposure width of the LED and LD serving also as a charge remover that electrically discharges the photosensitive member is narrower than the width of the photosensitive member, the edge of the photosensitive member is not electrically discharged. That is, the surface potential of the photosensitive member remains negatively charged. As a result, the potential difference (development potential) between the photosensitive member and the development is significant, worsening the background fogging or contamination of the non-image formation area of the photosensitive drum and hence causing unnecessary consumption of developing agent.
Consequently, the developing agent developed on the photosensitive member adheres to a secondary transfer roller via the intermediate transfer member, contaminating the back surface of the recording medium during the image forming operation on the recording medium. In order to avoid such difficulty, the width of the LED and the LD serving as the charge remover may have a width equal to or greater than the width of the photosensitive member. However, this configuration increases the cost and the space.
JP-3457083-B2 (JP-H08-234646-A) proposes ways in which the charge remover for the photosensitive member is controlled to suppress adherence of the developing agent onto a boundary between the non-exposure portion and the exposed portion (discharged portion) of the photosensitive member. The charge remover maintains an area in which a potential distribution changes gradually between the last discharge potential and a uniform charge potential. When the area enters a development process, a development bias is turned off.
JP-2013-218029-A proposes reducing the intensity of the transfer electrical field less than that during image transfer, when a non-charged surface of the photosensitive member (or a discharged surface) passes by the transfer position, thereby preventing unnecessary charging of the surface of the photosensitive member.
In JP-3457083-B2 (JP-H08-234646-A), adherence of developing agent to the photosensitive member is suppressed by preventing the potential difference from changing sharply at the boundary between the non-exposure portion and the exposed portion (discharged portion) of the photosensitive member when stopping driving of the photosensitive member.
In this configuration, adherence of the developing agent may be suppressed by discharging the photosensitive member when the photosensitive member is stopped. However, the size and the cost are still not reduced because the charge remover is disposed downstream from a primary transfer side of the photosensitive member.
In JP-2013-218029-A, when the non-charged surface of the photosensitive member faces transfer position, the intensity of the transfer electrical field is reduced less than that during image transfer. In other words, JP-2013-218029-A does not propose discharging the photosensitive member by intensifying the transfer electrical field of the transfer section.
In view of the above, there is demand for a charge removing mechanism to prevent contamination of the photosensitive member at a position outside the exposure portion with a width corresponding to the LED width while reducing the size and the cost.